Limb for surveying instruments



Oct. 15, 1929. w. L. EGY

\ LIME FOR SURVEYING INSTRUMENTS 2 Sheets-Sheet. 1

Filed Jan. 3, 1928 w W m l V/l/ard L. 59y 921 Oct. 15, 1929. w. EGY

LIMB FOR SURVEYING INSTRUMENTS Filed Jan. 3, 1928 2 Sheets-Shet 2 m m My z a F/ WM Pe -ca ca. is." 11 129 1.. new, or r1202, imw' purpose in fine instruments,-

, soft that the edges of the destroying the sharpness .cision instruments.

UNITED s TATEs' "rims-r.- arms YORK, nssienon 'ro w. a L; a; or new.

i YORK, A CORPORATION OF NEW YORK 111MB FOR SURVEYIQNG- TNS'IRU HENTS Application. Med January This invention relates to geometrical instruments and resides in improvements in the graduated limbs and verniers and the like forming parts of such instruments, and particularly those used in surveying instruments.

ceiving very fine sharp engraved 1ines,and is of a very desirable color for the purpose.

These advantages were considered so outstanding that, prior to the present invention, silver had displaced all other metals for this despite the Well known disadvantages residing in its use.

' Silver is relatively so expensive, and has such poor mechanical strength, that it must be mounted on some other support, and is so limbs must not be handled, else the e ges will become rounded, and accuracy of the readings against the verniers customarily used therewith. It tarnishes readily, arid when tarnished the engraved scale is illegible, particularly in poor lights.

The present invention is based on the dis covery that aknown alloy heretofore used in other arts merely for its lightness and high mechanical strength, offers an ideal combination of properties for this special field of use. It is inexpensive as compared with silver, and sinceit can be forged into the desired forms, the limbs can be made in one piece which directly receives the graduations. This is advantageous from the standpoint of manufacturing, simplicity and maintained accuracy. The alloy has a good texture when polished, does not tarnish from 'contact with the atmosphere, and can be as finely andas readily graduated as can silver. It is so hard that it resists wear, and when properly heattreated is peculiarly'fre'e from'any tendency to warp. V I

The freedom from Warping is a pro 'erty of peculiar importance in the limbs 0 pre- The bronze heretofore used is subject to warping, as is well known to instrument makers, and limbs formed of it often warp out of round or, out of plane; or both, with harmful results. The limb should 'a, 1928. Serial no. 244,290.

- run in plane the Slight departures from accuracy in this respect limit the precision of readings. If the b warps out of round after graduation the graduations themselves are inaccurate.

The alloy in question is an aluminum-base alloy described and claimed in the patent to Archer and J efiries, N 0. 1,472,739, dated October 30, 1923. Broadly stated, the alloy is free from copper, except as an impurityand contains magnesium and not less than 0.5%

silicon; preferably about 1.0% of each of magnesium and silicon. Specific, examples are given in the patent above identified. The alloy develops the desired physical properties for this use by being heated, quenched and artificially'aged as described in that patent.

Prior to my invention the high tensile strength, elongation and Brinell hardness of this alloy were known; but, so far as I am aware, its unusual property of receiving very sharp engravedlines,

' In practice blanks for the limbs'are pref+ erably die forged in one piece, and hence re- 7 quire a minimum of machine finishing, but they. might be out and shaped from forged, hammered, rolled, or other mechanically worked stock, in any known manner. The blanks are heated, quenched and artificially aged before machining, and, after machining. are'polished over the area to be graduated. They are engraved in ordinar dividing engines in the-usual manner. nfinished areasmay be lacquered if desired. In order to show difierent specific forms of limbs to which the invention is peculiarly iapplicable, it is illustrated in the accompanying drawing as embodied in a vertical limb Vernier with the edges as close-together as is mechanically possible.

its freedom in a truly remarkable degree from any appreciable neither been observed nor and vernier and in a horizontal limband vernier for a transit of known construction.

In the drawing,-

Fig. 1 is an elevation of the vertical limb and vernier.

i Fig. 2 is a section on the line 2-2 of Fig. 1.

Fig. 3 is a fragmentary section on the line 3+3 of Fig. 1.

Fig. 4 is a plan view of the horizontal limb and verniers.

Fig. 5 is a section on the line 5-5 of Fig. 4.

Referring first to Figs. 1, 2 and 3, the vertical circle in the example illustrated consists of a wheel having a central hub 6, radial 5 spokes 7 and rim 8. The hub is provided with a cruciform opening 9 Whose shape is dependent on the mode of mounting the circle on the telescope trunnion. The vertical circle is fixed in place on the trunnion by means of screws passing through the holes 11 which are formed with countersinks for the screw heads as clearly shown. The plane face 12 of the rim is machined and polished to give a good matte texture and the edge of the rim 5 is machined square with sharp edges, as indicated at 13 to run true against the vernier indicated generally by the numeral 14.

The groove 15 is a clearance groove to permit the periphery of the graduated portion oftherimtobemaehinedto a sharp edge. The vernier 14 is of the usualarcuate form and has a thin overhanging edge 16 opposed to the periphery of the limb. The vernier is mounted on the telescope standard (not shown) by screws threaded into the holes 17 Turning now to Figs. 4 and 5, a horizontal limb with two opposed verniers are shown, with all supporting parts omitted.

The limb 21 is saucer shaped, as shown in Fig. 5 and the inner edge 22, adjacent the graduations, is undercut to permit this edge 22 to be machined accurately with sharp square edges. The vernier 23 is also undercut so as to present' a relatively thin and squared projecting portion 24 in opposition to the inner periphery of the limb.

The limb 21 is open at its center and is formed with an annular shoulder 25 which centers it on thesupporting flange carried by a tapered quill shaft, not shown. The limb is attached to the flange by screws which pass through the holes 26 and these holes are I formed with countersinks for the screw heads, as is clearly shown.

N0 patentable invention is here claimed in volving the mode of mounting either the vernier or the limb, and consequently all such features have been omitted from the drawing.

After the limb, formed in either of the two ways above described, or in any other suitable way, has been machined, the face to be graduated is polished by known methods. and

then engine divided. No special procedure isnecessary in either of these operations. After the engraving operation (performed by the dividing engine) the graduations are filled to make them more legible, as is usual in this art.

Blanks for either type of limb, or for other types known in the art, may be die forged from this alloy and this practice is desirable because it produces a superior blank and one which requires a minimum of machine finishing. The blank may be formed, however, by cutting operations, provided the stock from which it is formed has been mechanically Worked to refine it. In any case, at some time in the process of manufacture, prior to the final machining operations, the material is heat-treated, that is. it is quenched from the proper temperature and then artificially aged as described in the patent above identified.

In the present specification and claims the term mechanically worked" is used as a generic term inclusive of forging, hammering and rolling operations practiced to refine and improve the homogeneity of the metal.

The resulting product has a mechanical strength far in excess of cast bronze heretofore almost universally used as a support for applied silver dials. The limb is devoid of any tendency to Warp and is so hard that wear on the graduated edge is negligible. color is good. The polished surface will not tarnish when exposed to air (it is affected by certain gases not ordinarily encountered, notably chlorine), can readily be graduated with lines as fine and as sharp as it is possible to produce on silver, and has the ad vantage of light weight.

The invention offers peculiar advantages in all graduated limbs including verniers, but is particularly advantageous in any graduated limb which is read against the vernier because the freedom from warping tendency allows the use of minute clearances and assures the maintenance of absolute trueness which not only facilitates accurate reading but assures the maintained accuracy of the graduations.

What is claimed is,

1. A graduated limb having its graduated face engraved in a mechanically worked, quenched, and artificially aged aluminumbase alloy, free from copper except as an impurity and containing magnesium and not less than 0.5% silicon.

2. A. graduated limb having its graduated face engraved in a mechanically worked, quenched, and artificially aged aluminumbase alloy, free from copper except as an impurity and containing about 1% magnesium and about 1% silicon.

3. A one-piece graduated lilnb composed of an aluminum 'base alloy free from copper except as an impurity and containing magnesium and not less than 0.5% silicon, forged to form, quenched, artificially aged, and hear- The ing graduations engraved directly in a polishe surface of the forging,

4. A. one-piece graduated limb composed of an aluminum base alloy free from no per except as an impurity and containing a out 1% magnesium and about 1% silicon, forged to form, quenched, artificially aged, and having raduations engraved directly in a polishe surface of the forgin r In testimony whereof have signed my 

